1. Technical Field
The present invention relates to a developing device for visualizing a latent image formed by a difference in electrostatic potential by applying toner to the latent image, a method of producing the developing device, and an image forming apparatus employing this developing device.
2. Related Art
In a developing device for forming a visual image by transposing toner to an electrostatic latent image on an image holding body, two-component developing agent having toner and magnetic carrier mixed or one-component developing agent having magnetic toner as a main component has been widely used. Such developing agent is magnetically attracted to a peripheral face of a developing roll, and transported to a position opposed to the image holding body. Then, a developing bias voltage is applied between the image holding body and the developing roll, and within an electric field which has been created, the toner is transferred to the electrostatic latent image on the image holding body thereby to form a visual image.
As the developing roll as described above, there has been widely used a developing roll including a magnet roll which is stably held so as not to rotate, and a thin sleeve in a cylindrical shape which is held around the magnetic roll so as to rotate. The magnet roll is magnetized with plural magnetic poles in a tangential direction, and magnetically attracts the magnetic toner or the magnetic carrier to a surface of the sleeve thereby to transport the developing agent in the tangential direction with rotation of the sleeve. On this occasion, the developing agent held on the sleeve forms a magnetic brush in which the magnetic toner or the magnetic carrier is continued in a shape of straw-stack, on the magnetic poles of the magnet roll. Particularly, on the developing magnetic pole which is provided at a position opposed to the image holding body, a large amount of toner is transposed onto the image holding body owing to the shape of straw-stack, whereby development with sufficient density is carried out.
Condition of the magnetic brush on the developing magnetic pole varies depending on distribution of magnetic flux density in vicinity of the position where the developing roll is opposed to the image holding body.
On the other hand, recently, in an image forming apparatus for forming an image using toner, it has been more and more desired to conduct a process at high speed, and an art of supplying a sufficient amount of developing toner to an image holding body which is rotating at high speed has been proposed.